A conventional navigation apparatus displays the current position of a vehicle which is determined by a vehicle position determining unit on a digital map (simply referred to as a “map” from here on) displayed on a display unit while superimposing the current position on the map. Furthermore, the conventional navigation apparatus searches for a recommended route from the current position of the vehicle which is determined by the vehicle position determining unit to a destination or a via-place (simply referred to as a “destination” from here on in this specification) which is inputted via an input unit, and displays the recommended route on the map. The conventional navigation apparatus then carries out a route guidance of the recommended route on the basis of the shapes of road links read from a recording medium.
By the way, recent years have seen increase in the number of cars owned by individuals and occurrence of traffic congestions in various parts of roads. Especially, most of vehicles travelling along a highway or expressway (simply referred to as a “highway” from here on in this specification) which is extending toward a big city and which is used for commuting or the like are occupied by only one person and this results in increase in traffic congestions. In order to solve this problem, there have been constructed highways where traffic is restricted by law according to the conditions of vehicles including the number of passengers and vehicle types.
For example, a car pool lane (Car Pool Lane) which is adopted by a road system mainly seen in big cities of North American is an example. A car pool lane is also called an HOV lane (High Occupancy Vehicle Lane), and is a lane along which, for example, only vehicles in each of which two or more persons are riding are granted to travel. For example, a lane which is also provided on a highway is known as a car pool lane. A road system which adopts such a car pool lane provides users with a preferential treatment that makes it possible to arrive at the destination in a shorter time when they travel along a car pool lane so as to prod users to share a vehicle with one or more persons, thereby reducing the traffic as a whole and therefore reducing traffic congestions.
As a technology relevant to such a car pool lane, patent reference 1 discloses a routing apparatus which implements more appropriate routing in order to deal with a case in which whether a vehicle is allowed to travel varies according to the conditions of the vehicle. This routing apparatus sets up a route to a destination in consideration of vehicle related information. For example, when the vehicle is occupied by one passenger or less, the routing apparatus handles car pool lanes as lanes along which the vehicle cannot travel and does not define them as a target for route determination, whereas when the vehicle is occupied by two or more passengers, the routing apparatus handles car pool lanes in the same way that the routing apparatus handles other roads, and defines them as a target for route determination. Therefore, when the vehicle is occupied by two or more passengers, the routing apparatus may set up a more advantageous route to the destination by including car pool lanes into the route, compared with a case in which it does not include any car pool lane into the route. Because in many cases car pool lanes are more advantageous than general purpose lanes, for example, car pool lanes are closer to exits and the travelled distance over which the vehicle travels along the route is reduced in the case of using car pool lanes, it can be expected that the route to the destination including car pool lanes becomes more appropriate.
Patent reference 2 discloses a navigation apparatus which enables a vehicle to efficiently travel along a lane from which the vehicle is restricted from exiting and then entering another lane and which the vehicle is restricted from entering from another lane. This navigation apparatus reads map data including road information about entering and exiting points in a highway provided with car pool lanes from a DVD, and stores them in a data buffer. A route search processing unit performs a route searching process in consideration of whether or not car pool lanes can be used by using the map data stored in the data buffer. When performing a route guidance using car pool lanes, a car pool lane guidance unit performs a predetermined lane change guidance using an image and voice at a time when each of the entering and exiting points at which the vehicle should change its travelling direction moves close to a point at a predetermined distance or less from the position of the vehicle.
Furthermore, patent reference 3 discloses a vehicle-mounted navigation apparatus which searches for a recommended route in consideration of the number of passengers. This vehicle-mounted navigation apparatus has a storage unit for storing map data including link data about each link which constructs a road on a map. As for a car pool link on which restrictions of prohibiting a vehicle which are not occupied by two or more persons from traveling are imposed, the vehicle-mounted navigation apparatus uses link data including information showing that such restrictions are imposed on the car pool link to search for a recommended route from the place of departure to the destination. Furthermore, when a car pool link is included in a constitution link which constructs the recommended route, the vehicle-mounted navigation apparatus receives an input of the number of passengers, and searches for a recommended route from the place of departure to the destination by using the link data to exclude links along which the vehicle cannot travel because the received number of passengers does not meet a certain criterion.    [Patent reference 1] JP,2000-131085,A    [Patent reference 2] JP,2001-183159,A    [Patent reference 3] JP,2005-061988,A
In many cases, a car pool lane currently provided is disposed as a central one of a plurality of lanes of a highway. A problem is therefore that when a vehicle enters a highway from a local street via an entrance of the highway or a connection road to the highway and then enters a car pool lane from an ordinary driving lane of the highway, the vehicle must cross a plurality of driving lanes of the highway until entering the car pool lane, and this entails danger to the driver of the vehicle and forces the driver to do a burdensome driving operation when many vehicles are travelling along the highway at a high speed and when a traffic congestion is occurring. Furthermore, because the number of vehicles which are travelling along a highway at a high speed changes greatly depending on what day of the week it is or what time zone it is, and low-acceleration vehicles and large-sized vehicles also travel along a highway, it is dangerous to cross a plurality of driving lanes during travel over a short distance. This problem similarly arises in a case in which a vehicle goes out of a car pool lane to a highway via an exit of the car pool lane, crosses an ordinary driving of the highway, and then goes out of the highway to a local street via an exit or a connection road of the highway.
However, no measures against the above-mentioned problem are taken in the route search of conventional navigation apparatuses, and conventional navigation apparatuses simply perform a search for a route including a car pool lane as a part thereof. Therefore, the problem that when a vehicle uses a car pool lane, that is, when a vehicle enters a car pool lane from a local street via ordinary driving lanes of a highway, and then goes out of the car pool lane to a local street via ordinary driving lanes of the highway, the vehicle has to cross a plurality of driving lanes of the highway, and this entails danger to the driver of the vehicle and also forces the driver to do a burdensome driving operation is left behind.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a navigation apparatus which can provide a recommended route which enables the user to use a car pool lane safely for the user.